As more fuel-efficient vehicles are pursued to protect the global environment, tires for vehicles with reduced rolling resistance are needed. For example, there has been proposed a tire with reduced rolling resistance which has a double-layer structure including a base tread (inner layer) with low energy loss and a cap tread (outer layer) with excellent abrasion resistance in the tread portion, which largely affects the rolling resistance.
In such a tire, reducing the amount of reinforcing agent in a rubber composition for a base tread is known to reduce the energy loss of the rubber composition, but such a method reduces the rubber stiffness and thus deteriorates the handling stability (steering performance). Further, with this method, even if the amount of vulcanizing agent such as sulfur is increased to enhance the stiffness, the durability tends to be poor.
Patent Literature 1 discloses a rubber composition for a base tread including certain amounts of a natural rubber, a butadiene rubber containing 1,2-syndiotactic polybutadiene crystals, a butadiene rubber synthesized in the presence of a rare earth catalyst, and a reinforcing agent, and exhibiting an improved property balance among fuel efficiency, handling stability, and durability. However, there still remains room for improvement in performance.